1. Technical Field
The present invention pertains generally to novel Neisseria meningitidis serogroup B glycoconjugates. More particularly, the invention pertains to glycoconjugates formed from a Neisseria meningitidis serogroup B capsular oligosaccharide derivative (MenB OS derivative) in which sialic acid residue N-acetyl groups have been replace with N-acyl groups, and methods of making and using those glycoconjugates.
2. Background of the Invention
Neisseria meningitidis is a causative agent of bacterial meningitis and sepsis. Meningococci are divided into serological groups based on the immunological characteristics of capsular and cell wall antigens. Currently recognized serogroups include A, B, C, D, W-135, X, Y, Z and 29E. The polysaccharides responsible for the serogroup specificity have been purified from several of these groups, including A, B, C, D, W-135 and Y.
N. meningitidis serogroup B (“MenB”) accounts for approximately 50 percent of bacterial meningitis in infants and children residing in the U.S. and Europe. The organism also causes fatal sepsis in young adults. In adolescents, experimental MenB vaccines consisting of outer membrane protein (OMP) vesicles have been found to be approximately 50% protective. However, no protection has been observed in vaccinated infants and children, the age groups at greatest risk of disease. Additionally, OMP vaccines are serotype- and subtype-specific, and the dominant MenB strains are subject to both geographic and temporal variation, limiting the usefulness of such vaccines.
Effective capsular polysaccharide-based vaccines have been developed against meningococcal disease caused by serogroups A, C, Y and W135. However, similar attempts to develop a MenB polysaccharide vaccine have failed due to the poor immunogenicity of the capsular MenB polysaccharide (termed “MenB PS” herein). MenB PS is a homopolymer of (N-acetyl (α2→8) neuraminic acid. Escherichia coli K1 has the identical capsular polysaccharide. Antibodies elicited by MenB PS cross-react with host polysialic acid (PSA). PSA is abundantly expressed in fetal and newborn tissue, especially on neural cell adhesion molecules (“NCAMs”) found in brain tissue. PSA is also found to a lesser extent in adult tissues including in kidney, heart and the olfactory nerve. Thus, most anti-MenB PS antibodies are also autoantibodies. Such antibodies therefore have the potential to adversely affect fetal development, or to lead to autoimmune disease.
MenB PS derivatives have been prepared in an attempt to circumvent the poor immunogenicity of MenB PS. For example, C4–C8 N-acyl-substituted MenB PS derivatives have been described. See, EP Publication No. 504,202 B, to Jennings et al. Similarly, U.S. Pat. No. 4,727,136 to Jennings et al. describes an N-propionylated MenB PS molecule, termed “NPr-MenB PS” herein. Mice immunized with NPr-MenB PS glycoconjugates were reported to elicit high titers of IgG antibodies. Jennings et al. (1986) J. Immunol. 137:1708. In rabbits, two distinct populations of antibodies, purportedly associated with two different epitopes, one shared by native MenB PS and one unshared, were produced using the derivative. Bactericidal activity was found in the antibody population that did not cross react with MenB PS. Jennings et al. (1987) J. Exp. Med. 165:1207. The identity of the bacterial surface epitope(s) reacting with the protective antibodies elicited by this conjugate remains unknown.
Although the above-described MenB PS derivatives are capable of eliciting a significant anti-MenB PS response, responding antibodies still include a significant proportion of molecules that are cross-reactive with polysialic acid residues in host tissue, and therefore autoreactive. Thus, to date, no approach which has been taken with respect to MenB vaccine development has been succesful in providing a safe and effective vaccine against MenB. Accordingly, there remains a need to provide MenB immunogens which can be used in vaccine formulations, wherein the immunogens do not elicit the production of antibodies in immunized animals that are cross-reactive with host tissue and can be thus used in the prevention or treatment of MenB disease.